Field of the Invention
The present disclosure relates to the field of analysis of the condition of interior surface of tubulars. More particularly, the present disclosure relates to the determination of the condition of the inner surfaces of tubulars, for example piping carrying fluids, including well bore tubulars, wherein the condition of the tubular is determined by passing a multi-arm caliper device through the tubular, and the condition of the tubular is inferred from the measurement data received from the multi arm caliper.
Description of the Related Art
Multi-arm caliper tools are widely used to evaluate or inspect the interior condition of tubular, such as piping, as well as in the field of cased hole wireline logging in order to determine the geometric properties of the inner surface of tubulars such as casing, liners or tubings. Multi-arm calipers are provided with a plurality of caliper arms extending around a longitudinal centerline or axis of the tool, such that radii extending from the centerline of the tool to the adjacent tubular inner surface may be measured at a plurality of angular locations around the tool longitudinal axis at a relatively high frequency using caliper arms extending from the body of the tool, and these measurements are recorded in the tool and/or transmitted along a wireline to a remote location for recording or analysis. The data is used to assess the integrity of interior surface or wall the tubular, and can be used to locate areas of wall erosion, kinks, abnormal bending, or other geometric physical indicia of impending loss of the fluid sealing integrity of the tubular. If the tool data indicates an issue with the integrity of the wall or inner surface of the tubular, the owner or operator of the equipment or well in which the tubular is used can take remedial steps, such as locating a liner over the location of the tubular in which there is an integrity issue, replacing the tubular (such as where a secondary tubing was extended into, but not cemented into place, in a well bore, or the tubular is in process equipment and can be accessed for replacement) or sealing off the location in the tubular where the integrity issue is present. Where the tubular is a casing or liner permanently fixed in a well bore, and the well is still producing, the owner or operator of the well will need to determine whether the cost of drilling an additional well to the producing formation location is economically profitable if the well is closed off.
In one multi-arm caliper tool where the tool is pulled or pushed within the tubular, the tool includes mechanical probe arms that contact the inner surface of the tubular and mechanically transfer the radial geometric variations of the tubular to a transducer individually associated with each arm that in turn translates the mechanical variations of the distance from the tip of the arm in contact with the inner surface of the tubular to the tool housing or tool centerline into electric signals that are fed to a data processing and transmission system, which may be on-board the tool or which may be transmitted, via a wireline, to a remote location such as a surface location where a casing in a well bore is being evaluated. Alternately the signal may be simply recorded within a recorder that is located within or in the vicinity of the caliper tool as part of the downhole tool.
To translate the mechanical movement of the probe into an electrical signal, the probe is interconnected to a transducer such as a linear variable differential transformer, otherwise known as an LVDT, wherein movement of the mechanical probe tip at the end of the probe and in contact with the inner surface of the tubular causes movement of a magnet within an electric field of the transducer. As the magnet moves in the field, it causes perturbations thereof, which are sensed by secondary coils and the resulting changes in the electric field are converted to electric signals representative of the distance the magnet has moved in the LVDT, and, thus changes in the relative position of the end of the probe arm (tip) in contact with the inner surface of the tubular are converted into an electric signal. As the tool traverses a tubular in a well bore, it encounters different ambient temperatures, which, because of the mechanical nature of the tool cause changes in length of the various physical components thereof, as well drift in the electrical components. To address this drift, users of such downhole caliper tools use approximations of drift based on surface measured calibrations of the tool over a temperature range to compensate for temperature effects on the tool. For example, the effect of temperature on the caliper measurements may be corrected using digital processing using a numeric model of the measurement temperature drift. However, it has been found that these correction factors can result in erroneous readings. Where the erroneous readings indicate an impending loss of integrity of the tubular such as casing, expensive retrofitting of a sealing sleeve or coating over the indicated location, or plugging of the tubular at and below the location and closing off of the producing well, will occur when it is unnecessary to do so, resulting in significant unnecessary expenditure. Where an erroneous reading fails to detect an integrity issue, the tubular can fail leading to the leakage of the fluids therein into the adjacent environment.
Thus, there is a need for a multi-arm caliper tool which more reliably compensates for temperature change along the length of the tubular being evaluated.